knowledge

类的初始化

the definition of class

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class ClassName:
	<statement-1>
	.
	.
	.
	<statement-N>

a simple example

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# two ways without parameters
class MyClass:
	i = 12345
	def f(self):
		return 'hello world'
#the other way is instantiation
class MyClass:
    def __init__(self):
        self.data = []

含参的类

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class High_school_student():
    
    school = "BUPT" 
	
    def __init__(self,age,sex):
		self.age = age
		self.sex = sex
studen1 = High_school_student(18,'M')
print("The age of student is"+str(student1.age))
print(student1.school)

类的私有化

通过在属性成员的名称前加下滑线”__“实现成员的私有化

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class High_school_student():
	def __init__(self,age,sex)
		self.__age = age
		self.__aex = sex
student1 = High_school_student(18,'M')
print("The age of student is"+str(student.age))

得到的结果是

image-20221026104659804

但是私有化成员并非不可访问，可以通过_类名__私有变量的方式来进行访问

image-20221026105330360

另外除了属性成员(attribute references),方法(method)也可进行私有化

类的继承(Inheritance)

The syntax for a derived class definition looks like this：

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class DeriveClassName(BaseClassName):
	<statement-1>
	.
	.
	.
	<statement-N>:
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class people:
	# define basic attribute
	name = ' '
	age = 0
	# define private attribute
	__weight = 0
	# define methods
	def __init__(self,n,a,w):
		self.name = n
		self.age = a
		self.__weight = w
	def speak(self):
		print("%s 说: 我 &d 岁。"%(self.name,self.age))
# inheritance
class student(people):
	grade = ''
	def __init__(self,n,a,w,g):
		#调用父类的构造函数
		people.__init__(self,n,a,w)
		self.grade = g
	#覆盖父类的方法
	def speak(self)；
		print("%s 说：我 %d 岁了，我在读%d年级"%(self.name,sekf.age,self,grade))

s = student('ken',10,60,3)
s.speak()

image-20221026111905952

Practice

定义一个名为Circle的类，该类表示圆形，它的属性有center和radius，其中center是一个Point对象，而radius是一个数。

实例化一个Circle对象，来表示一个圆心在(150,100),半径为75的圆形。

编写一个函数point_in_circle接收一个Circle对象和一个Point对象，并党Point处于Circle的边界或其界内时，返回True

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import math

class Point():
    def __init__(self,x,y):
        self.x =x
        self.y =y
    
class Circle():
    def __init__(self,x,y,radius):
        self.center = Point(x,y)
        self.radius = radius
    def distance(self,p1,p2):
      #距离可以采用两点横纵坐标之差的根号下平方和的形式
    	dist = math.sqrt((p1-self.center.x)**2+
                         (p2-self.center.y)**2)
        return dist
    
circle1 = Circle(150,100,75)
point1 = Point(100,100)

def point_in_circle(C1,P1):
   	#用distance方法求得圆心和点间的距离
    dist = C1.distance(P1.x,P1.y)
    #如果两点间距离小于半径则返回True
    if C1.radius>=dist:
        return True
    else :
        return False
output = point_in_circle(circle1,point1)
print(output)